Effect of Fungicide and Timing of Application on Management of Phoma Black Stem of Cultivated Sunflowers in the United States.

Phoma black stem (PBS), caused by Phoma macdonaldii Boerema (teleomorph Leptosphaeria lindquistii Frezzi), is the most common stem disease of sunflower (Helianthus annuus L.) in the northern Great Plains region of the United States. However, the impact of PBS on sunflower yield in the United States is unclear, and a near complete absence of information on the impact of fungicides on disease management exists. The objectives of this study were to determine the impact of PBS on sunflower yield, the efficacy of available fungicides, the optimal fungicide application timing, and the economic viability of fungicides as a management tool. Fungicide timing efficacy was evaluated by applying single and/or sequential applications of pyraclostrobin fungicide at three sunflower growth stages in 10 field trials between 2017 and 2019. Efficacy of 10 fungicides from the Fungicide Resistance Action Committee (FRAC) groups 3, 7, and 11 were evaluated in four field trials between 2018 and 2019. The impact of treatments on PBS were evaluated by determination of incidence, severity, maximum lesion height, disease severity index (DSI), and harvested yield. Nine of the 10 fungicides evaluated and all fungicide timings that included an early bud application resulted in disease reductions when compared with the nontreated controls. The DSI was negatively correlated to sunflower yield in high-yield environments (P = 0.0004; R2 = 0.3425) but not in low- or moderate-yield environments. Although FRAC 7 fungicides were generally most efficacious, the sufficient efficacy and lower cost of FRAC 11 fungicides make them more economically viable in high-yielding environments at current market conditions.

Management of Soybean Cyst Nematode and Sudden Death Syndrome with Nematode-Protectant Seed Treatments Across Multiple Environments in Soybean.

As soybean (Glycine max) production continues to expand in the United States and Canada, so do pathogens and pests that directly threaten soybean yield potential and economic returns for farmers. One such pathogen is the soybean cyst nematode (SCN; Heterodera glycines). SCN has traditionally been managed using SCN-resistant cultivars and rotation with nonhost crops, but the interaction of SCN with sudden death syndrome (SDS; caused by Fusarium virguliforme) in the field makes management more difficult. Nematode-protectant seed treatments have become options for SCN and SDS management. The objectives of this study were to evaluate nematode-protectant seed treatments for their effects on (i) early and full season SCN reproduction, (ii) foliar symptoms and root-rot caused by SDS, and (iii) soybean yield across environments accounting for the above factors. Using a standard protocol, field trials were implemented in 13 states and one Canadian province from 2019 to 2021 constituting 51 site-years. Six nematode-protectant seed treatment products were compared with a fungicide + insecticide base treatment and a nontreated check. Initial (at soybean planting) and final (at soybean harvest) SCN egg populations were enumerated, and SCN females were extracted from roots and counted at 30 to 35 days postplanting. Foliar disease index (FDX) and root rot caused by the SDS pathogen were evaluated, and yield data were collected for each plot. No seed treatment offered significant nematode control versus the nontreated check for in-season and full-season nematode response, no matter the initial SCN population or FDX level. Of all treatments, ILEVO (fluopyram) and Saltro (pydiflumetofen) provided more consistent increases in yield over the nontreated check in a broader range of SCN environments, even when FDX level was high.

Foliar Fungicides Containing FRAC 11 Mitigate Phomopsis Stem Canker in Sunflower (Helianthus annuus).

Phomopsis stem canker reduces yield of sunflower (Helianthus annuus L.) up to or exceeding 40%; however, management recommendations have not been developed for U.S. farmers. Between 2009 and 2020, foliar fungicide trials were conducted in Minnesota, Nebraska, North Dakota, and South Dakota for a total of 49 location-years. Random effects meta-analyses were performed on the disease severity index (DSI) and yield data collected from the foliar fungicide trials to determine the overall and individual effectiveness of the tested fungicides. Effect sizes, Cohen's f or Hedges' g, were calculated as the difference in DSI or yield between the fungicide treatment and nontreated control (NTC) divided by the pooled SD. The pooled Cohen's f for DSI and yield was 0.40 (95% CI = [0.29, 0.42]), indicating a large effect size and that fungicide treatments had a significant effect on DSI and yield (P < 0.0001). Among the fungicide groups, quinone outside inhibitor (QoI) (DSI [k = 45; g = -0.47] and yield [k = 46; g = 0.41]) is moderately effective and premixes of demethylation inhibitors (DMI), succinate dehydrogenase inhibitors (SDHI), and QoI (DMI + SDHI + QoI) (DSI [k = 3; g = -0.79] and yield [k = 3; g = 0.94]) are largely effective in comparison with NTC. Upon performing prediction analyses, the probability of not recovering the fungicide application cost (Ploss) associated with QoI (pyraclostrobin) was <0.35 for a range of sunflower grain prices suggesting a greater probability of return on investment from a single application of fungicide. Overall, our study suggests that the use of QoI fungicides is likely to be profitable in the presence of Phomopsis stem canker (DSI > 5%).

Multiple Species of Asteraceae Plants Are Susceptible to Root Infection by the Necrotrophic Fungal Pathogen Sclerotinia sclerotiorum.

The necrotrophic fungal pathogen Sclerotinia sclerotiorum can cause disease on numerous plant species, including many important crops. Most S. sclerotiorum-incited diseases of crop plants are initiated by airborne ascospores produced when fungal sclerotia germinate to form spore-bearing apothecia. However, basal stalk rot of sunflower occurs when S. sclerotiorum sclerotia germinate to form mycelia within the soil, which subsequently invade sunflower roots. To determine whether other plant species in the Asteraceae family are susceptible to root infection by S. sclerotiorum, cultivated sunflower (Helianthus annuus L.) and seven other Asteraceae species were evaluated for S. sclerotiorum root infection by inoculation with either sclerotia or mycelial inoculum. Additionally, root susceptibility of sunflower was compared with that of dry edible bean and canola, two plant species susceptible to S. sclerotiorum but not known to display root-initiated infections. Results indicated that multiple Asteraceae family plants are susceptible to S. sclerotiorum root infection after inoculation with either sclerotia or mycelium. These observations expand the range of plant hosts susceptible to S. sclerotiorum root infection, elucidate differences in root inoculation methodology, and emphasize the importance of soilborne infection to Asteraceae crop and weed species.

Characterization of Virulence Phenotypes of Soybean Cyst Nematode (Heterodera glycines) Populations in North Dakota.

Soybean cyst nematode (SCN; Heterodera glycines) continues to be the greatest threat to soybean production in the United States. Because host resistance is the primary strategy used to control SCN, knowledge of SCN virulence phenotypes (HG types) is necessary for choosing sources of resistance for SCN management. To characterize SCN virulence phenotypes in North Dakota, a total of 419 soybean fields across 22 counties were sampled during 2015, 2016, and 2017. SCN was detected in 42% of the fields sampled, and population densities in these samples ranged from 30 to 92,800 eggs and juveniles per 100 cm3 of soil. The SCN populations from some of the infested fields were virulence-phenotyped with seven soybean indicator lines and a susceptible check ('Barnes') using the HG type tests. Overall, 73 SCN field populations were successfully virulence-phenotyped. The HG types detected in North Dakota were HG types 0 (frequency rate: 36%), 7 (27%), 2.5.7 (19%), 5.7 (11%), 1.2.5.7 (4%), and 2.7 (2%). However, before this study only HG type 0 was detected in North Dakota. The designation of each of these HG types detected was also validated by repeating the HG type tests for 33 arbitrarily selected samples. This research for the first time reports several new HG types detected in North Dakota and confirms that the virulence of SCN populations is shifting and overcoming resistance, highlighting the necessity of using different resistance sources, rotating resistance sources, and identifying novel resistance sources for SCN management in North Dakota.

A Greenhouse Method to Evaluate Sunflower Quantitative Resistance to Basal Stalk Rot Caused by Sclerotinia sclerotiorum.

Resistance of sunflower to basal stalk rot (BSR) caused by the fungus Sclerotinia sclerotiorum is quantitative, controlled by multiple genes contributing small effects. Consequently, artificial inoculation procedures allowing sufficient throughput and resolution of resistance are needed to identify highly resistant sunflower germplasm resources and to map loci contributing to resistance. The objective of this study was to develop a greenhouse-based method for evaluating sunflower quantitative resistance to BSR that would be simple, space- and time-efficient, high throughput, high resolution, and correlated with field observations. Experiments were conducted with 5-week-old sunflower plants and Sclerotinia-infested millet seed as inoculum to assess the impact of pot size and temperature and to determine the most favorable inoculum rate and placement. Subsequently, an additional experiment was performed to assess the correlation of the greenhouse inoculation procedure with field results by using a panel of 32 sunflower genotypes with known field response to BSR previously determined in multiyear, multilocation artificially inoculated trials. Experimental observations indicated that the newly developed greenhouse inoculation procedure provided improved resolution to identify highly resistant genotypes and was strongly correlated with field observations. This method will be useful for screening of sunflower experimental and breeding materials, disease phenotyping of genetic mapping populations, and evaluation of resistance to different pathogen isolates.

Meta-Analysis of Soybean Yield Response to Foliar Fungicides Evaluated from 2005 to 2018 in the United States and Canada.

Random-effect meta-analyses were performed on data from 240 field trials conducted between 2005 and 2018 across nine U.S. states and Ontario, Canada, to quantify the yield response of soybean after application of foliar fungicides at beginning pod (R3) stage. Meta-analysis showed that the overall mean yield response when fungicide was used compared with not applying a fungicide was 2.7% (110 kg/ha). Moderator variables were also investigated and included fungicide group, growing season, planting date, and base yield, which all significantly influenced the yield response. There was also evidence that precipitation from the time of planting to the R3 growth stage influenced yield when fungicide was used (P = 0.059). Fungicides containing a premix of active ingredients from multiple groups (either two or three ingredients) increased the yield by 3.0% over not applying a fungicide. The highest and lowest yield responses were observed in 2005 and 2007, respectively. Better yield response to fungicides (a 3.0% increase) occurred when soybean crops were planted not later than 21 May and when total precipitation between planting and the R3 application date was above historic averages. Temperatures during the season did not influence the yield response. Yield response to fungicide was higher (a 4.7% increase) in average yield category (no spray control yield 2,878 to 3,758 kg/ha) and then gradually decreased with increasing base yield. Partial economic analyses indicated that use of foliar fungicides is less likely to be profitable when foliar diseases are absent or at low levels.

Quantitative PCR Assays Developed for Diaporthe helianthi and Diaporthe gulyae for Phomopsis Stem Canker Diagnosis and Germplasm Screening in Sunflower (Helianthus annuus).

Phomopsis stem canker of sunflower is caused by two fungal pathogens, Diaporthe helianthi and Diaporthe gulyae, in the United States. In this study, two quantitative PCR (qPCR) assays were developed to detect and quantify D. helianthi and D. gulyae in sunflower. The two assays differentiated the two fungi from each other, other species of the genus Diaporthe, and pathogens, and they have high efficiency (>90%). The qPCR assays detected the two pathogens on plant samples exhibiting Phomopsis stem canker symptoms sampled from commercial sunflower fields in Minnesota, Nebraska, North Dakota, and South Dakota. Furthermore, the assays were used to screen cultivated sunflower accessions for resistance to D. helianthi and D. gulyae. The disease severity index (DSI) of the accessions significantly correlated (P < 0.0001) with the amount of pathogen DNA from the qPCR assays. The qPCR assays identified PI664232 and PI561918 to be significantly less susceptible (P ≤ 0.05) to D. helianthi and D. gulyae, respectively, when compared with the susceptible check cultivar HA 288, and this was in agreement with the DSI. These results suggest that the qPCR assays for D. helianthi and D. gulyae can be used as a reliable tool to diagnose Phomopsis stem canker and screen sunflower germplasm for disease resistance.

Determination of Virulence Phenotypes of Plasmopara halstedii in the United States.

Downy mildew, caused by Plasmopara halstedii (Farl.) Berl. and de Toni, is an economically important disease in cultivated sunflowers, Helianthus annuus L. Resistance genes incorporated into commercial hybrids are used as an effective disease management tool, but the duration of effectiveness is limited as virulence evolves in the pathogen population. A comprehensive assessment of pathogen virulence was conducted in 2014 and 2015 in the U.S. Great Plains states of North Dakota and South Dakota, where approximately 75% of the U.S. sunflower is produced annually. The virulence phenotypes (and races) of 185 isolates were determined using the U.S. standard set of nine differentials. Additionally, the virulence phenotypes of 61 to 185 isolates were determined on 13 additional lines that have been used to evaluate pathogen virulence in North America and/or internationally. Although widespread virulence was identified on several genes, new virulence was identified on the Pl8 resistance gene, and no virulence was observed on the PlArg, Pl15, Pl17 and Pl18 genes. Results of this study suggest that three additional lines should be used as differentials and agree with previous studies that six lines proposed as differentials should be used in two internationally accepted differential sets. For effective disease management using genetic resistance, it is critical that virulence data be relevant and timely. This is best accomplished when pathogen virulence is determined frequently and by using genetic lines containing resistance genes actively incorporated into commercial cultivars.

Comprehensive Disease Survey of U.S. Sunflower: Disease Trends, Research Priorities and Unanticipated Impacts.

Between 2002 and 2015, a comprehensive survey of sunflower fields across seven Midwestern U.S. states was conducted 12 times and continues to be conducted every other year. The surveyors collected data on yield, agronomic management factors, disease, insect, weed, and bird damage. All surveyors were volunteers and came from universities (extension and research staff), USDA-ARS, and seed and chemical companies. In the 12 years the survey was conducted, data from 2,267 fields were collected. The results are presented annually at the National Sunflower Association Research Forum and are used to set sunflower research priorities. While 10 diseases are surveyed annually, we focus this article on the importance, findings, implications, and impacts of the five most important: downy mildew, Phomopsis stem canker, rust, Rhizopus head rot, and Sclerotinia head rot. This survey is unique among field crops in both scope and scale, and this manuscript discusses salient and clandestine benefits of intense and long-term disease surveys.

Evaluation of Oxathiapiprolin for the Management of Sunflower Downy Mildew.

Downy mildew is a yield-limiting disease of sunflower, caused by the pathogen Plasmopara halstedii. Zoospore infection of root tissue shortly after planting results in systemic infection, causing postemergence damping off or severe stunting and head sterility. Although fungicide-applied seed treatments can be an effective management tool, the pathogen is resistant to phenylamide fungicides in many growing regions, and other available fungicides have limited efficacy. Oxathiapiprolin, the first member of the piperidinyl thiazole isoxazoline fungicides, was evaluated for efficacy on downy mildew in field trials conducted from 2011 to 2015 in North Dakota. Throughout the course of the study, the rate range was narrowed from active ingredient (a.i.) at 0.45 to 116.0 µg a.i. seed-1 to an optimal effective rate of 9.37 to 18.75 µg a.i. seed-1. Within that optimal range, the downy mildew incidence of sunflower planted with oxathiapiprolin-treated seed was significantly lower than the incidence in the nontreated sunflower in all 11 trials with disease pressure. Additionally, downy mildew incidence of sunflower planted with oxathiapiprolin-treated seed was significantly lower than sunflower planted with competitive commercially available fungicide-treated seed in 10 of those 11 trials. The use of oxathiapiprolin by sunflower growers is likely to reduce disease incidence and subsequent yield loss to downy mildew.

Oomycete Species Associated with Soybean Seedlings in North America-Part II: Diversity and Ecology in Relation to Environmental and Edaphic Factors.

Soybean (Glycine max (L.) Merr.) is produced across a vast swath of North America, with the greatest concentration in the Midwest. Root rot diseases and damping-off are a major concern for production, and the primary causal agents include oomycetes and fungi. In this study, we focused on examination of oomycete species distribution in this soybean production system and how environmental and soil (edaphic) factors correlate with oomycete community composition at early plant growth stages. Using a culture-based approach, 3,418 oomycete isolates were collected from 11 major soybean-producing states and most were identified to genus and species using the internal transcribed spacer region of the ribosomal DNA. Pythium was the predominant genus isolated and investigated in this study. An ecology approach was taken to understand the diversity and distribution of oomycete species across geographical locations of soybean production. Metadata associated with field sample locations were collected using geographical information systems. Operational taxonomic units (OTU) were used in this study to investigate diversity by location, with OTU being defined as isolate sequences with 97% identity to one another. The mean number of OTU ranged from 2.5 to 14 per field at the state level. Most OTU in this study, classified as Pythium clades, were present in each field in every state; however, major differences were observed in the relative abundance of each clade, which resulted in clustering of states in close proximity. Because there was similar community composition (presence or absence) but differences in OTU abundance by state, the ordination analysis did not show strong patterns of aggregation. Incorporation of 37 environmental and edaphic factors using vector-fitting and Mantel tests identified 15 factors that correlate with the community composition in this survey. Further investigation using redundancy analysis identified latitude, longitude, precipitation, and temperature as factors that contribute to the variability observed in community composition. Soil parameters such as clay content and electrical conductivity also affected distribution of oomycete species. The present study suggests that oomycete species composition across geographical locations of soybean production is affected by a combination of environmental and edaphic conditions. This knowledge provides the basis to understand the ecology and distribution of oomycete species, especially those able to cause diseases in soybean, providing cues to develop management strategies.

Oomycete Species Associated with Soybean Seedlings in North America-Part I: Identification and Pathogenicity Characterization.

Oomycete pathogens are commonly associated with soybean root rot and have been estimated to reduce soybean yields in the United States by 1.5 million tons on an annual basis. Limited information exists regarding the frequency and diversity of oomycete species across the major soybean-producing regions in North America. A survey was conducted across 11 major soybean-producing states in the United States and the province of Ontario, Canada. In 2011, 2,378 oomycete cultures were isolated from soybean seedling roots on a semiselective medium (CMA-PARPB) and were identified by sequencing of the internal transcribed spacer region of rDNA. Sequence results distinguished a total of 51 Pythium spp., three Phytophthora spp., three Phytopythium spp., and one Aphanomyces sp. in 2011, with Pythium sylvaticum (16%) and P. oopapillum (13%) being the most prevalent. In 2012, the survey was repeated, but, due to drought conditions across the sampling area, fewer total isolates (n = 1,038) were collected. Additionally, in 2012, a second semiselective medium (V8-RPBH) was included, which increased the Phytophthora spp. isolated from 0.7 to 7% of the total isolates. In 2012, 54 Pythium spp., seven Phytophthora spp., six Phytopythium spp., and one Pythiogeton sp. were recovered, with P. sylvaticum (14%) and P. heterothallicum (12%) being recovered most frequently. Pathogenicity and virulence were evaluated with representative isolates of each of the 84 species on soybean cv. Sloan. A seed-rot assay identified 13 and 11 pathogenic species, respectively, at 13 and 20°C. A seedling-root assay conducted at 20°C identified 43 species as pathogenic, having a significantly detrimental effect on the seedling roots as compared with the noninoculated control. A total of 15 species were pathogenic in both the seed and seedling assays. This study provides a comprehensive characterization of oomycete species present in soybean seedling roots in the major production areas in the United States and Ontario, Canada and provides a basis for disease management and breeding programs.

Phomopsis Stem Canker: A Reemerging Threat to Sunflower (Helianthus annuus) in the United States.

Phomopsis stem canker causes yield reductions on sunflower (Helianthus annuus L.) on several continents, including Australia, Europe, and North America. In the United States, Phomopsis stem canker incidence has increased 16-fold in the Northern Great Plains between 2001 and 2012. Although Diaporthe helianthi was assumed to be the sole causal agent in the United States, a newly described species, D. gulyae, was found to be the primary cause of Phomopsis stem canker in Australia. To determine the identity of Diaporthe spp. causing Phomopsis stem canker in the Northern Great Plains, 275 infected stems were collected between 2010 and 2012. Phylogenetic analyses of sequences of the ribosomal DNA internal transcribed spacer region, elongation factor subunit 1-α, and actin gene regions of representative isolates, in comparison with those of type specimens, confirmed two species (D. helianthi and D. gulyae) in the United States. Differences in aggressiveness between the two species were determined using the stem-wound method in the greenhouse; overall, D. helianthi and D. gulyae did not vary significantly (P≤0.05) in their aggressiveness at 10 and 14 days after inoculation. These findings indicate that both Diaporthe spp. have emerged as sunflower pathogens in the United States, and have implications on the management of this disease.

Phenotypic Diversity of Puccinia helianthi (Sunflower Rust) in the United States from 2011 and 2012.

Puccinia helianthi, causal agent of sunflower rust, is a macrocyclic and autoecious pathogen. Widespread sexual reproduction of P. helianthi was documented in North Dakota and Nebraska for the first time in 2008 and has since frequently occurred. Concurrently, an increase in sunflower rust incidence, severity, and subsequent yield loss on sunflower has occurred since 2008. Rust can be managed with resistance genes but determination of virulence phenotypes is important for effective gene deployment and hybrid selection. However, the only P. helianthi virulence data available in the United States was generated prior to 2009 and consisted of aggregate virulence phenotypes determined on bulk field collections. The objective of this study was to determine the phenotypic diversity of P. helianthi in the United States. P. helianthi collections were made from cultivated, volunteer, and wild Helianthus spp. at 104 locations across seven U.S. states and one Canadian province in 2011 and 2012. Virulence phenotypes of 238 single-pustule isolates were determined on the internationally accepted differential set. In total, 29 races were identified, with races 300 and 304 occurring most frequently in 2011 and races 304 and 324 occurring most frequently in 2012. Differences in race prevalence occurred between survey years and across geography but were similar among host types. Four isolates virulent to all genes in the differential set (race 777) were identified. The resistance genes found in differential lines HA-R3 (R4b), MC29 (R2 and R10), and HA-R2 (R5) conferred resistance to 96.6, 83.6, and 78.6% of the isolates tested, respectively.

Effect of Fungicide and Timing of Application on Management of Sunflower Rust.

Sunflower rust is an important yield-limiting disease in sunflower production in the Great Plains of the United States. Rust severity and incidence have increased between 2002 and 2011, and genetic resistance is limited in most commercial hybrids, particularly the high-value confectionary market type. Although fungicides are available for rust management in the United States, management recommendations are insufficient. Specifically, efficacy and timing data are very limited for fungicides in FRAC groups 7 and 11. Seventeen fungicide efficacy and timing trials were conducted between 2008 and 2011 in North Dakota. Timings evaluated across the four years included single or multiple applications at growth stages (GS): GS V8-V12 (late vegetative), GS R1 (terminal bud formation), GS R3-4 (elongation of bud), GS R5 (flowering), and GS R6 (completion of flowering). With few exceptions, fungicide applications of DMIs and QoIs controlled disease greater than SDHI fungicides. Fungicide applications made at R5, either singly or in combination, consistently resulted in greater disease control. A negative correlation (r = -0.7756) between disease control and yield was observed, resulting in a yield reduction of 6.6% for every 1% increase in disease severity.

Ascochyta blight in North Dakota field pea: the pathogen complex and its fungicide sensitivity.

Worldwide, Ascochyta blight is caused by a complex of host-specific fungal pathogens, including Ascochyta pisi, Didymella pinodes, and Didymella pinodella. The application of foliar fungicides is often necessary for disease management, but a better understanding of pathogen prevalence, aggressiveness, and fungicide sensitivity is needed to optimize control. Leaf and stem samples were obtained from 56 field pea production fields in 14 counties in North Dakota from 2017 to 2020 and isolates were collected from lesions characteristic of Ascochyta blight. Based on fungal characteristics and sequencing the ITS1-5.8S-ITS2 region, 73% of isolates were confirmed to be D. pinodes (n = 177) and 27% were A. pisi (n = 65). Across pathogens, aggressiveness was similar among some isolates in greenhouse assays. The in vitro pyraclostrobin sensitivity of all D. pinodes isolates collected from 2017 to 2020 was lower than that of the three baseline isolates. Sensitivity of 91% of A. pisi isolates collected in 2019 and 2020 was lower than the sensitivity of two known sensitive isolates. Resistance factors (Rf) from mean EC50 values of pyraclostrobin baseline/known sensitive isolates to isolates collected from 2017 to 2020 ranged from 2 to 1,429 for D. pinodes and 1 to 209 for A. pisi. In vitro prothioconazole sensitivity of 91% of D. pinodes isolates collected from 2017 to 2020 was lower than the sensitivity of the baseline isolates and 98% of A. pisi isolates collected from 2019 to 2020 was lower than the sensitivity of the known sensitive isolates. Prothioconazole Rf ranged from 1 to 338 for D. pinodes and 1 to 127 for A. pisi. Based on in vitro results, 92% of D. pinodes and 98% of A. pisi isolates collected displayed reduced-sensitivity/resistance to both fungicides when compared to baseline/known sensitive isolates. Disease control under greenhouse conditions of both pathogens provided by both fungicides was significantly lower in isolates determined to be reduced-sensitive or resistant in in vitro assays when compared to sensitive. Results reported here reinforce growers desperate need of alternative fungicides and/or management tools to fight Ascochyta blight in North Dakota and neighboring regions.

Application of image processing and transfer learning for the detection of rust disease.

Plant diseases introduce significant yield and quality losses to the food production industry, worldwide. Early identification of an epidemic could lead to more effective management of the disease and potentially reduce yield loss and limit excessive input costs. Image processing and deep learning techniques have shown promising results in distinguishing healthy and infected plants at early stages. In this paper, the potential of four convolutional neural network models, including Xception, Residual Networks (ResNet)50, EfficientNetB4, and MobileNet, in the detection of rust disease on three commercially important field crops was evaluated. A dataset of 857 positive and 907 negative samples captured in the field and greenhouse environments were used. Training and testing of the algorithms were conducted using 70% and 30% of the data, respectively where the performance of different optimizers and learning rates were tested. Results indicated that EfficientNetB4 model was the most accurate model (average accuracy = 94.29%) in the disease detection followed by ResNet50 (average accuracy = 93.52%). Adaptive moment estimation (Adam) optimizer and learning rate of 0.001 outperformed all other corresponding hyperparameters. The findings from this study provide insights into the development of tools and gadgets useful in the automated detection of rust disease required for precision spraying.

Developing Public-Private Partnerships in Plant Pathology Extension: Case Studies and Opportunities in the United States.

Public-private partnerships (PPPs) can be an effective and advantageous way to accomplish extension and outreach objectives in plant pathology. The greatest opportunities for extension-focused PPPs may be in response to large-scale or emerging disease management concerns or in addressing complex issues that impact agriculture, such as climate change, digital technology, and public perception of science. The most fertile ground for forming PPPs is where the needs and strengths of the public and private sectors are complementary. Developing PPPs depends as much on professional relationships as on technical skills or contracts. Defining and making room for the success of all partners, identifying and addressing barriers to success, and earning and maintaining trust are components that contribute to the effectiveness of PPPs. Case studies in plant pathology demonstrate the positive impact PPPs can have on partners and stakeholders and provide guidance on the formation of PPPs in the future.

Gene cloning using degenerate primers and genome walking.

Gene cloning is the first step of targeted gene replacement for functional studies, discovery of gene alleles, and gene expression among other applications. In this chapter, we will describe a cloning technique suitable for fungal species where the genomic information and sequences available are limited. This strategy involves obtaining protein sequences of the gene of interest from various organisms to identify at least two conserved regions. Degenerate primers are designed from these two conserved regions and the resulting PCR products are sequenced. The sequence of the PCR products can be analyzed using suitable databases to determine their similarity to the gene/protein of interest. In cases where the entire gene cannot be cloned directly using these primers, this initial nucleotide sequence can be used as a template for further primer design and genome walking in both directions for either the cloning of a longer fragment or even the cloning of the complete gene. Here, we describe the partial cloning of a reducing polyketide synthase gene from the fungal plant pathogen Ascochyta rabiei using this strategy.